For example, Patent Literature 1 discloses this kind of ink jet recording apparatus. Patent Literature 1 discloses an ink droplet detecting device in which a light emitting module and a light receiving module are fixed to a base member, the angle of the light emitting module can be adjusted in the vertical direction, and the movement of the light receiving module can be adjusted in the horizontal direction, so that the optical axis is adjusted. In the ink droplet detecting device, ink droplets are sequentially discharged from an ink droplet discharge head while the ink droplet discharge head is moved, a laser beam is emitted from the light emitting module so as to collide with the flying ink droplet, and the discharge state of the ink droplet, such as a discharge failure or deflection, is detected from a variation in the amount of light received by the light receiving module.
In the ink jet recording apparatus disclosed in Patent Literature 1, after the ink droplet detecting device is assembled to the recording apparatus body, the optical axis between the light emitting element and the light receiving element of the ink droplet detecting device is adjusted.